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6/11/2026
The LivingCare Group
It depends on the injection, and the evidence gives a different picture for each. For steroid injections, NICE says they "only provide short-term relief (2 to 10 weeks)" [2]. For hyaluronic acid, PRP and Arthrosamid, independent research has not settled on a figure - so where the evidence is thin, this article says so rather than offering a number.
Knee osteoarthritis is common. Arthritis UK estimates that around 4.6 million people in England have it - a modelled estimate, for England alone [1]. Here is what the evidence says about four knee injections LivingCare offer, and what it does not. For the condition itself, see Knee Arthritis.
Between 2 and 10 weeks, on NICE's figure. Its osteoarthritis guideline asks clinicians to "explain to the person that these only provide short-term relief (2 to 10 weeks)" [2]. A steroid (corticosteroid) injection is the knee injection with the clearest published duration.
Other authoritative sources word it differently, and each is worth reading on its own terms:
These come from different sources written for different purposes, so they sit side by side rather than combine into one range. None of them is a prediction for any one knee.
Whether repeated steroid injections affect the joint itself is a separate question, covered in our article Do Steroid Injections Damage The Joint?
There is no independent, evidence-based figure to give. Hyaluronic acid injections - properly known as viscosupplementation injections - have been studied in many trials, but the independent reviews do not put a number of weeks or months on them.
A scientific study called a meta-analysis was published in the BMJ in 2022; it considered 169 trials and concluded that viscosupplementation "was associated with a small reduction in pain intensity compared with placebo" [3]. Another 2024 review of 18 randomised trials concluded that the injections "may reduce pain in the short term" [4]. Neither review was funded by a manufacturer [3][4], and neither gives a duration of expected benefit.
Mr Paul Sutton, the consultant who reviewed this article, gives his clinical view:
"HA is a biologic substance and after injection is broken down in the knee joint so it is not likely to last more than a few months at most." - Mr Paul Sutton, Consultant Orthopaedic Surgeon
The independent evidence does not yet give a reliable figure. PRP (platelet-rich plasma) is prepared from a sample of the patient's own blood and injected into the joint [5].
A 2025 systematic review of 28 randomised trials and 3,246 patients, with no funding and no competing interests declared, graded its evidence using GRADE - a standard scale for how confident researchers can be in a finding [5]. For pain, certainty was rated moderate when PRP was compared with placebo, and very low when it was compared with steroid injections [5]. That second rating means the evidence cannot say whether PRP works as well as or lasts longer than a steroid injection. The authors of this study add that "long-term follow-up data in existing studies remain insufficient" [5].
Independent evidence on Arthrosamid is limited, and it does not establish a duration. Arthrosamid is a polyacrylamide hydrogel injected into the knee [6].
An independent 2025 study, which received no funding, followed 269 patients (314 knees) for up to 24 months [6]. It had no comparison group, and its authors are clear about what that means: "There was no control group, hence placebo effect could not be determined." [6] In plain terms, the study cannot show how much of any change came from the injection itself.
How many people in England have knee osteoarthritis? Arthritis UK estimates around 4.6 million people in England have knee osteoarthritis. It is a modelled estimate rather than a count of diagnoses, and it covers England only [1].
When does a knee steroid injection have its greatest effect? A 2026 practice article in the Canadian Medical Association Journal describes a "peak response at 1 to 2 weeks" [7]. NICE describes the effect as short-term, lasting 2 to 10 weeks [2].
Which knee injection lasts the longest? The independent evidence cannot say. Steroid is the only one of the four with a duration published by NICE [2]. The 2025 PRP review rated its comparison with steroid injections as very low certainty [5], and no independent study cited here establishes a duration for hyaluronic acid or Arthrosamid.
Is a knee injection a permanent fix? Not on the independent evidence available. NICE describes steroid injections as short-term [2], the authors of the 2025 PRP review say long-term follow-up data "remain insufficient" [5], and the independent Arthrosamid study had no control group [6].
How long an injection lasts is one question among several. What is causing the pain, what has already been tried, and what each option involves are the others, and they are answered at an assessment rather than in an article. A Pain Management Consultation runs at Thorpe Park Clinic in Leeds and Canon Medical Arena in Sheffield. For injections elsewhere in the body, including the spine, read What Injection Options Might A Pain Specialist Discuss With You? Exceptional care, without the wait.
Medically reviewed by: Mr Paul Sutton, Consultant Orthopaedic Surgeon
This article is for general information and is not sponsored content.
